Synaptic scaling is thought to be important in maintaining the stability of networks during development and activity-dependent plasticity. Under certain pathological conditions, such as epilepsy, the balance of excitation and inhibition is greatly perturbed, suggesting a lack of homeostatic scaling. Therefore, understanding synaptic scaling is crucial for understanding how neurons transfer information and remain plastic under normal and neuropathological conditions. Synaptic scaling has been observed in rat visual cortex as a result of development and monocular deprivation, suggesting that scaling is important in the activity-dependent refinement of circuits. However, studies have been limited by the inability to selectively block scaling and leave other forms of plasticity intact, and so the precise role of scaling in activity-dependent development and plasticity remains unclear. Scaling can be blocked in single cultured cortical neurons with an RNAi hairpin that targets the AMPA receptor subunit, GluR2, suggesting that GluR2 is critical for expression of scaling. This proposal will determine if GluR2 is also essential for scaling down in response to chronic heightened activity and which domain of the GluR2 subunit is required for its regulatory role in scaling. This proposal will also address whether scaling can be blocked in vivo with a conditional GluR2 knockout mouse model. Being able to block scaling in vivo is critical for elucidating the role of scaling in activity-dependent development. These questions will be persued using whole-cell voltage-clamp recordings of miniature excitatory postsynaptic currents (mEPSCs) in cultured cortical cells and acute slices containing layer 2/3 primary visual cortex. Together, the experiments proposed here will (1) further characterize the molecular regulation of synaptic scaling in cultured cortical cells, (2) develop a paradigm for selectively blocking scaling with high spatial and temporal resolution in vivo, and with this paradigm, (3) describe the role of synaptic scaling in experience-dependent development and plasticity in intact visual cortex. PUBLIC HEALTH RELEVANCE: Synaptic scaling is thought to be important in maintaining the stability of neural networks. Many neurological disorders, such as epilepsy, Rett Syndrome, and autism, are characterized by a perturbation in the balance of excitation and inhibtion, perhaps suggesting a deficit in homeostasic scaling. These studies will examine the mechanism and role of synaptic scaling in the intact nervous system, which may provide insight into the pathological processes that result in these disorders.